The present invention is related to the field of semiconductor fabrication and more particularly to a method of monitoring and controlling metallization using percent backsputtering as a control parameter to achieve low contact resistance and interface void-free metal layer.
In the field of semiconductor fabrication, the use of copper metallization for high speed semiconductor devices is becoming increasingly prevalent. In a typical copper metallization process, a barrier layer is deposited over an underlying first copper layer using a physical vapor deposition (PVD) process. Referring to FIG. 1, a diagram of a metal sputtering tool 100 (also referred to herein as metal sputtering chamber 100) is presented.
In the depicted embodiment, sputtering tool 100 includes a chassis 102 that defines a chamber 101 and encloses a sputter target 104 that is comprised at least partially of a material to be deposited on a wafer surface. Sputter target 104 may include tantalum, tantalum nitride, titanium, titanium nitride, copper, or other metal elements suitable for use in a semiconductor interconnect structure.
The depicted embodiment of sputtering tool 100 is characteristic of commercially distributed ionized metal plasma deposition tools such as the Endura(copyright) line of sputtering tools from Applied Materials, Inc. A DC power supply 106 provides a bias to sputtering target 104 while a rotating magnetic assembly 116 provides a magnetic field within chamber 101 of sputtering tool 100. In addition, a radio frequency (RF) power supply 108 energizes a coil 109 within chamber 101. A platform 112 within chamber 101 is connected to an AC power supply 110. In one embodiment, RF power supply 108 operates at a frequency of approximately 2 MHz and an AC power supply 110 operates at a frequency of approximately 13.56 MHz.
As depicted in FIG. 1, a wafer 120 is placed within chamber 101. In one embodiment, wafer 120 is displaced above pedestal 112 by one or more electrically insulating buttons 114 typically comprised of a ceramic material. In other embodiments, wafer 120 may rest directly upon platform 112.
In the depicted embodiment, a gas inlet 116 provides means for introducing one or more source gases 118 into chamber 101 during deposition. Suitable source gasses 118 may include inert species such as argon, xenon, or helium as well as other source gases including nitrogen.
As an inert species such as argon is released into chamber 101, RF power source 108 generates a plasma that includes charged argon particles which are attracted to the target 104 by DC bias 106. As the relatively heavy argon particles strike target 104, target particles are released into chamber 101 where a certain percentage of the particles are charged in the plasma generated by RF source 108. These charged particles (as well as a certain percentage of uncharged target particles) traverse chamber 101 and are deposited on wafer 120.
The power used for DC power supply 106 and RF power supply 108 are typically in excess of 1000 W and can result in the generation of highly energetic particles. In addition, the plasma itself is generally sustained at a temperature of approximately 300xc2x0 C. The combination of the highly energetic particles and plasma thermal energy can result in significant localized heating of the wafer where the sputter material is deposited. In the case of sputter depositing a barrier material such as tantalum over a metal such as copper, it is theorized that the localized heating may result in recrystallization of the copper or thermal expansion and subsequent contraction of the copper thereby resulting in the formation of voids beneath the tantalum layer.
Attempts at correlating the occurrence of such voids to conventional parameters such as the AC power applied during tantalum deposition have been generally unsuccessful in eliminating the formation of voids. It would therefore be desirable to correlate the occurrence of voids during a biased metallization process to a quantifiable parameter and to implement a method of characterizing and qualifying a sputtering tool 100 based on the determined parameter. It would be further desirable if implemented solution did not significantly increase the cost and complexity of the metallization process.